Occurrence of metallo-b-lactamases in Pseudomonas aeruginosa clinical isolates resistant to carbapenems

Abstract number: 1733_178

Vitti D., Protonotariou E., Sofianou D.

Objectives: The main mechanism of resistance to carbapenems is the production of metallo-b-lactamases (MBLs). These enzymes are plasmid-mediated and their spread in P. aeruginosa has become of great concern. The aim of this study was to determine the occurrence of MBLs in clinical isolates of P. aeruginosa resistant to carbapenems in our hospital.

Methods: A total of 36 nonrepetitive strains of P. aeruginosa resistant to carbapenems were obtained from clinical specimens between February 2003 to November 2005. The identification and susceptibility testing were performed by the VITEK-2 automated system (bioMérieux, France). Imipenem (IMP) and Meropenem (MER) MICs were determined by E-test. EDTA-IMP double disc synergy test was carried out for screening of MBLs production. All isolates were subjected to PCR assay with specific primers and DNA sequencing. Pulsed-field gel electrophoresis (PFGE) was used to delineate clonal relationship between strains.

Results: Among the 36 carbapenem-resistant isolates of P. aeruginosa, 18 were positive by PCR for the presence of blaVIM. All these isolates had MIC of IMP and MER >32 mg/mL and showed a synergy between EDTA-IMP. Sequence analysis of PCR product revealed the presence of VIM-2 gene. Eight VIM producing strains harboured also a blaSHV gene and gave a synergy using disks of amoxicillin+clavulanate and 3rd generation cefalosporins. Phylogenetic tree using UPGMA (pairwise-unweighted) algorithm with QuantityOne Software (BIORAD), revealed different PFGE patterns with predominance of type A that comprised 5 isolates.

Conclusions: This study illustrates the spread of genes encoding MBLs in P. aeruginosa. High percentage of MBLs-producing strains were, in addition, SHV-producers. Appropriate control measures including introduction of MBL screening in regular basis, are necessary in order to prevent wider dissemination of these genes.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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